Langerhans cell histiocytosis (LCH) is a rare histiocytic tumour in adult.We report a case of LCH involving skull bones in a 35year old lady who presented with fever, headache and diabetes insipidus since two years.Radiological examination revealed osteolytic lesions in the parietal and Electro occipital bones along with a solid, enhancing lesion in the pituitary infundibulum.Osteolytic lesions showed ttypical histomorphology of Thermocouple Thermometers LCH on light microscopy and on IHC it was positive for SI 00 but negative for CD1 a.LCH with CD1 a negativity is very rare and hence we are presenting this case.